CESSNA SECTION 4
MODEL 172S NAV III NORMAL PROCEDURES
GFC 700 AFCS
U.S.
FUEL VAPOR PROCEDURES
The engine fuel system can cause fuel vapor formation on the ground
during warm weather. This will generally occur when the outside
ambient air temperature is above 80°F. Vapor formation may increase
when the engine fuel flows are lower at idle and taxi engine speeds.
The following procedures are recommended when engine idle speed
and fuel flow fluctuations show that fuel vapor may be present:
1. With the mixture full rich, set the throttle at 1800 RPM to 2000
RPM. Maintain this power setting for 1 to 2 minutes or until
smooth engine operation returns.
2. Retard the throttle to the idle stop to verify normal engine
operation.
3. Advance the throttle to 1200 RPM and lean the mixture as
described under FUEL SAVINGS PROCEDURES FOR FLIGHT
TRAINING OPERATIONS.
4. In addition to the above procedures, the auxiliary fuel pump may
be turned ON with the mixture adjusted as required to aid vapor
suppression during ground operations. The auxiliary fuel pump
should be turned OFF prior to takeoff.
5. Just prior to TAKEOFF, apply full throttle for approximately 10
seconds to verify smooth engine operation for takeoff.
When the engine is operated above 1800 RPM, the
resulting increased fuel flow results in lower fuel
temperatures throughout the engine fuel system. This
increased flow purges the fuel vapor and the cooler fuel
minimizes vapor formation.
In addition to the previous procedures, the sections below should be
reviewed, and where applicable, adhered to:
Section 3 -Take note of the excessive fuel vapor procedures in both
the checklist and the amplified procedures sections.
Section 4 -Take note of the hot weather operational notes and
procedures in both the checklist and the amplified
procedures sections.
172SPHBUS-01
4-27
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